Conventional Diesel engines are provided with a fuel injection system which is configured to dispose in a combustion chamber of the engine a metered quantity of fuel. Fuel injection system includes a high pressure fuel pump, that increases the pressure of the fuel received from a low pressure pump in fluid communication with a fuel tank, and that delivers the fuel to a fuel rail in fluid communication with a fuel injector disposed within the combustion chamber of the engine. The high pressure pump is provided with a digital inlet valve for selectively admitting fuel to an inlet conduit of the high pressure pump.
A known digital inlet valve includes a shutter associated to a shutter seat provided in the inlet conduit of the high pressure pump. The shutter can translate from a closed to an open position in contrast with the action of a compression spring. The translation of the shutter is operated by a linear electromagnetic actuator, also known as linear solenoid, which includes a needle located inside a coil winding. The needle is biased by the action of a compression (return) spring towards a lower position, where it contacts the shutter keeping it in the open position.
When an electric current flows through the coil winding it generates a magnetic field that operates the translation of the needle in contrast to the return spring. In this way the needle departs from the shutter allowing the same to move in the closed position where it is received in the shutter seat, preventing the flowing of the fuel.
A drawback of the disclosed digital inlet valve is due to the noise generated during its operation. In detail the noise is due to the operation of the shutter and the needle during the closing and the opening phases of the inlet valve.
Accordingly, it is desirable to reduce the operating noise of the digital inlet valve with a simple, rational and rather inexpensive solution.